The active matrix organic light-emitting diode (AMOLED) is becoming one of research focuses in the technical field of panel displays. Comparing with a liquid crystal display (LCD), an organic light-emitting diode (OLED) has advantages of low energy consumption, low production cost, self luminescence, wide viewing angle and fast response. Until now, the OLED has begun to take place of the traditional LCD screen in a display field of cell phone, personal digital assistant (PDA), digital camera, and etc. The design of the pixel driving circuit is an essential technical field for the AMOLED, and is of great research significance.
In contrast to control brightness by steady voltage in the TFT-LCD, it is necessary for the light emitting to be controlled by steady current in the OLED since the OLED is driven by the current. Due to manufacture process and aging of devices, a voltage threshold (Vth) for driving a thin-film transistor in each pixel may be drifted, which leads to a variation of the current running through the OLED of each pixel with a variation of the voltage threshold. As a result, the display brightness is not in uniform and degrades the display of a whole image.
Until now, a technique of in-cell touch has been successfully implemented in the LCD display. The in-cell touch not only has good touch sensitivity and functions as a capacitor-type touch may have, but also has a particular advantage, i.e. being not limited by a size of a screen, and thus plays an important role in a big-size touching screen. In addition, in the in-cell touch, the touching not only may be implemented by a finger, but also may be implemented by a laser pointer remotely.
Thus, in the display field, it is a tendency to integrate the in-cell touch with the AMOLED in the future.